Arsenal have had a £20 million bid ($33.29 million) rejected by Sporting Lisbon for William Carvalho, Goal can reveal.

The Gunners are working on a deal to capture the versatile midfielder in the final fortnight of the transfer window.

However, Arsenal's pursuit is complicated by Carvalho's third-party ownership, Sporting's £28m valuation and their own need to navigate a tricky Champions League qualifying tie against Besiktas.

The Gunners are expected to return with an improved offer for the 22-year-old, although the complex nature of the negotiations mean they are likely to go down to the wire.

Sporting are ready to cash in on Carvalho although, according to reports in Portugal, 40 per cent of his rights are owned by investment firm Banco Espirito Santo. The player is also represented by super agent Jorge Mendes, which has added a layer of difficulty to discussions taking place between the parties.

Arsene Wenger has sanctioned a formal move for Carvalho as he seeks to further strengthen his squad in the midfield anchorman and centre-back positions.

The Portugal international started his career in central defence although he is now used more regularly in midfield.

Arsenal are also closing in on an £8m deal to sign Olympiakos centre-back Kostas Manolas, and their move for Carvalho is understood to be in addition to the expected capture of the Greece international.

The London club's willingness to push the boat out for Carvalho could be influenced strongly by the outcome of their Champions League play-off tie against Besiktas, with victory paving the way for a minimum windfall of around £25m.